Wen-Cheng Liao

Many prediction models have been developed to address the disadvantages of creep, which is induced by aconstant load on concrete structures, such as cracks, deflections, serviceability failures, and reduced long-termperformance. However, the available models still lack accuracy in predicting the compressive creep of concrete,particularly in the case of self-compacting concrete (SCC), which differs from conventional concrete in itscomposition. Therefore, the model B4TW-SCC was calibrated using the B4 model to meet the SCC databaserequirements. The optimization of the new prediction model was carried out by evaluating statistical factors andthe weighting plan, which subdivided the 266 test curves in the laboratory database into independent variables.The developed prediction model performed better than the other models, based on both the SCC database andexperimental results in this study, which were conducted on the creep behaviour of SCC containing fly ash indifferent contents, 20% and 40% by mass of cementitious material.

Testing of concrete panels subjected to pure in-plane shear loading is necessary to elucidate the shear behavior of concrete. However, available data for predicting the shear capacity and behavior of steel fiber-reinforced concrete are rather limited. This study aims to evaluate the shear capacity and behavior of fiber-reinforced concrete made of highly flowable strain hardening fiber-reinforced concrete (HF-SHFRC) experimentally and analytically, respectively, using a panel tester loaded under pure shear and modified compression field theory (MCFT). The test was conducted using a panel test machine at the University of Toronto. The test results of the HF-SHFRC demonstrated strain hardening behavior at tension after the first crack, as indicated by the increase in the shear stress after the first crack in the HF-SHFRC panel. An analysis procedure is proposed for predicting the shear strength of steel fiber-reinforced concrete (SFRC) based on experimental data of the SFRC panels to obtain reliable results. A comparison of results obtained from the proposed analysis procedure and experiments show that it accurately predicted the response of the HF-SHFRC. The proposed MCFT-based analysis procedure can provide valuable insight for understanding the behavior of the SFRC panels under shear loading.

White building components, whether decorative or the overall structure, are susceptible to extreme weathering conditions, which affect the durability of the building’s external surface. In particular, white natural stone materials can provide buildings with beauty, durability, and sustainability, but this beauty is affected by key factors determining their weather resistance, namely physical properties such as porosity and acid and alkali resistances. As indicated by a past study, marble used as the exterior wall of a building in a similar environment will exhibit tarnishing after six months of weathering. Taiwan is a subtropical island, so the weather resistance of building materials to this environment is worthy of attention. As pointed out by the study, raw stone materials containing zirconium and silica can have greater weather resistance, do not easily change color, and possess good stress resistance properties. Focusing on this, this study attempted to identify stone materials with such compositions and sent samples to SGS (Societe Generale de Surveillance S.A., New Taipei City, Taiwan) for testing of weather resistance. This paper uses Spanish artificial stones for the study and observes the changes in the surface cleanliness on two buildings in Yilan County and Taipei in Taiwan after exposure to sun and rain. The experiments were conducted over two years. The study results showed that the artificial stones displayed no change in outward appearance under both rainy and acid rain environments. In Yilan, construction of an exterior wall was carried out in February 2018. The exterior wall used the white artificial stone directly from the manufacturer, and the black artificial stone with added paint for stone protection. After two months, the black artificial stone covered with paint exhibited a change in color and stains appeared on the surface, while the white artificial stone not covered with paint maintained the same cleanliness after two years. In Taipei, white Spanish artificial stone was used for the exterior wall of an entire building block in February 2020. After the frame was dismantled in September 2020, the color was found to be unaffected, being as pure white as it was when new. Therefore, this study selected Spanish artificial stone for the design of a building’s exterior wall, as the cleanliness of the stone surface is not affected and it has good applicability in rainy and acid rain island environments.

A concrete-filled steel tube (CFT) combines the advantages of concrete and steel in construction and structural applications. However, research on the time-dependent deformation of the CFT under long-term sustained loading are still limited, particularly for stress transfer between the steel tube and concrete due to creep. This study investigated the creep behavior of CFT over a long period of 400 days. The creep and shrinkage strain of CFT was significantly lower than those of concrete that was not confined within a steel tube. The vertical strains of the steel tube and concrete core were almost identical, and it was shown that they were well bonded and acted as a composite. The vertical stress of steel increased by 32.7%, whereas the vertical stress of concrete decreased by 15.8% at 375 days. The stress transfer is notable and cannot be neglected in CFT design. Moreover, the results of creep and shrinkage were compared to prediction values of the B4 model and B4-TW model to verify their validity.

Tensile strength is one of the important mechanical properties of concrete, but it is difficult to measure accurately due to the brittle nature of concrete in tension. The three widely used test methods for measuring the tensile strength of concrete each have their shortcomings: the direct tension test equipment is not easy to set up, particularly for alignment, and there are no standard test specifications; the tensile strengths obtained from the test method of splitting tensile strength (American Society for Testing and Materials, ASTM C496) and that of flexural strength of concrete (ASTM C78) are significantly different from the actual tensile strength owing to mechanisms of methodologies and test setup. The objective of this research is to develop a new concrete tensile strength test method that is easy to conduct and the result is close to the direct tension strength. By applying the strut-and-tie concept and modifying the experimental design of the ASTM C78, a new concrete tensile strength test method is proposed. The test results show that the concrete tensile strength obtained by this proposed method is close to the value obtained from the direct tension test for concrete with compressive strengths from 25 to 55 MPa. It shows that this innovative test method, which is precise and easy to conduct, can be an effective alternative for tensile strength of concrete.

The modulus of elasticity of concrete (E_c ) is an important factor in the design of RC structures. E_c is also essential for engineers to estimate deflections and stiffness of RC members. The prediction and calculation of E_c in Taiwan are still referred to ACI318-14 or ACI363R-92. It was confirmed that E_c is usually overestimated due to smaller coarse aggregate amount and higher paste volume in Taiwan. To obtain precise E_c , it is necessary to develop prediction equations that can reflect material characteristic of Taiwan. This study collects 1389 test data sets of E_c in Taiwan. By regression analysis with certain key parameters, such as silica fume, new and practical prediction equations based on ACI318-14 and ACI363R-92 are proposed. The proposed estimation formula improves the average value and the standard deviation of E_c-predict – to- E_c-test ratio of normal-strength concrete from 122% to 99%, and from 0.173 to 0.139, respectively; Similar observation can also be found relative to high-strength concrete (The average value of E_c-predict – to- E_c-test ratio of high-strength improves from 132% to 101%, and the standard deviation fell from 0.149 to 0.11). These equations reflect the low E_c characteristics in Taiwan and can provide a more accurate estimation of E_c for normal-strength and high-strength RC member designs.

Conducting research on steel fiber-reinforced concrete (SFRC) beams without stirrups, particularly the SFRC beams with high-strength concrete (HSC) and high-strength steel (HSS) reinforcing bars is essential due to the limitation of test results of high strength SFRC beams with high strength steel reinforcing bars. Eight shear strength prediction equations for analysis and design of the SFRC beam derived by different researchers are summarized. A database was constructed from 236 beams. Accordingly, the previous shear strength equations can be evaluated. Ten high-strength SFRC beams subjected to monotonic loading were prepared to verify the existing shear strength prediction equations. The equations for predicting shear strength of the SFRC beam are proposed on the basis of observations from the test results and evaluation results of the previous shear strength equations. The proposed shear strength equation possesses a reasonable result. For alternative analysis and design of the SFRC beams, ACI 318-19 shear strength equation is modified to consider steel fiber parameters.

Remarkable development of high-strength concrete and reinforcement has been achieved nowadays. The purpose of the New Reinforced Concrete (New RC) project is aimed to reduce member section size by using high-strength concrete (f′c > 70 MPa) and high-strength rebars (fy > 685 MPa). Material consumption can be further reduced owing to the upgrade of strength. However, the brittle nature of high-strength concrete may also cause early cover spalling and other ductility issues. The addition of steel fibers is an alternative transverse reinforcement in New RC infrastructure systems. Highly flowable strain-hardening fiber-reinforced concrete (HF-SHFRC) has excellent workability in the fresh state and exhibits the strain-hardening and multiple-cracking characteristics of high-performance fiber-reinforced cementitious composites (HPFRCC) in their hardened state. This study aims to investigate the cyclic behavior of New RC bridge columns made of HF-SHFRC. Five large-scale bridge columns are subjected to cyclic lateral loading to verify their responses and deformation capacity. The test results show that by adding 1.5 % of high-strength hooked steel fibers, great deformation capacity is developed, in which either the stirrups spacing is increased to two times that of the control specimen or all tires are eliminated in New RC bridge columns. In addition, the accuracy of the proposed concept of equivalent lateral reinforcement is verified by the test results. Implementation of HF-SHFRC in New RC infrastructure offers opportunities to significantly simplify the design and construction of members for sustainable urbanization while ensuring adequate ductility and damage tolerance.